WO2021023137A1

WO2021023137A1 - Lithium-ion battery and device

Info

Publication number: WO2021023137A1
Application number: PCT/CN2020/106475
Authority: WO
Inventors: 梁成都; 付成华; 韩昌隆; 陈培培
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2019-08-08
Filing date: 2020-07-31
Publication date: 2021-02-11
Also published as: CN112349962A; US20220158246A1; EP3989325A1; CN112349962B; EP3989325A4

Abstract

Provided are a lithium-ion battery and device. The lithium-ion battery comprises a battery housing, an electrolyte, and an electrode assembly. The electrolyte comprises a lithium salt and an organic solvent, and the electrode assembly consists of a positive electrode plate, a negative electrode plate, and a separator film. The positive electrode plate comprises a positive electrode current collector and a positive electrode membrane arranged on at least one surface of the positive electrode current collector and comprising a positive electrode active material; the negative electrode plate comprises a negative electrode current collector and a negative electrode membrane arranged on at least one surface of the negative electrode current collector and comprising a negative electrode active material. The lithium salt comprises one or more of the compounds represented by formula I, wherein n is an integer from 1 to 3, Rf₁ and Rf₂ are C_mF_2m+1, wherein m is an integer from 0 to 5, Rf₁ and Rf₂ are the same or different, and the group margin of the lithium-ion battery is 85%-95%. The lithium-ion battery has the advantages of good cycle performance, good rate performance, high safety performance, and good low-temperature discharge performance.

Description

Lithium ion battery and device

This application claims the priority of a Chinese patent application filed with the Chinese Patent Office on August 8, 2019, with an application number of 201910728961.7 and an application title of "lithium ion battery", the entire content of which is incorporated into this application by reference.

Technical field

This application relates to the field of battery technology, and in particular to a lithium ion battery and device.

Background technique

Lithium-ion batteries are widely used in electric vehicles and consumer electronic products due to their advantages of high energy density, high output power, long cycle life and low environmental pollution. The current market demand for lithium-ion batteries requires not only the advantages of high power, long cycle life, and long storage life, but also high energy density.

With the development of lithium-ion batteries towards miniaturization and light weight, the requirements for energy density are getting higher and higher. At present, in the prior art, in order to improve the energy density of lithium-ion batteries, the commonly adopted solution is as follows: compact the active material in the electrode as much as possible, so that the battery can accommodate more under the premise of the same volume and space. Electrode active materials, such as the increasingly higher coating weight of the pole piece and the larger and larger group margin design, lead to a series of problems such as deterioration of the charging power performance and discharge power performance of lithium-ion batteries, and poor cycle life. Therefore, it is necessary to provide a lithium ion battery with high energy density, low impedance, good dynamic performance and high safety factor.

Summary of the invention

In view of the problems in the background art, the purpose of this application is to provide a lithium-ion battery and device. The lithium-ion battery has the advantages of high energy density, good cycle performance, and good rate performance. At the same time, the lithium-ion battery also has the advantages of Good low-temperature discharge performance and safety performance.

In order to achieve the above objective, the present application provides a lithium ion battery, which includes a battery casing, an electrolyte, and an electrode assembly. The electrolyte includes a lithium salt and an organic solvent, and the electrode assembly is composed of a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode membrane which is arranged on at least one surface of the positive electrode current collector and includes a positive electrode active material. The negative electrode sheet includes a negative electrode current collector and a positive electrode film which is arranged on at least one surface of the negative electrode current collector and includes a negative electrode active material. Material negative diaphragm. The lithium salt includes one or more of the compounds represented by formula I, wherein n is an integer within 1 to 3, Rf ₁ and Rf ₂ are C _m F _2m+1 , where m is within 0 to 5. Rf ₁ and Rf _{2 are the} same or different, and the group margin of the lithium ion battery is 85%-95%.

This application includes at least the following beneficial effects:

The lithium ion battery of the present application includes one or more of the imine-type lithium salts shown in formula I, which can make the lithium ion battery have the advantages of good cycle performance, good rate performance, high safety performance, and good low-temperature discharge performance. .

On the basis of using the imine-type lithium salt shown in Formula I, the lithium ion battery of the present application also has the advantage of high energy density by adjusting the group margin of the lithium ion battery.

The device of this application includes the lithium ion battery provided in this application, and therefore has at least the same advantages as the lithium ion battery of this application.

Description of the drawings

In order to explain the technical solutions of the embodiments of the present application more clearly, the following will briefly introduce the drawings that need to be used in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. A person of ordinary skill in the art can obtain other drawings based on the drawings without creative work.

FIG. 1 is a schematic diagram of an embodiment of a lithium ion battery;

Figure 2 is an exploded view of Figure 1;

Fig. 3 is a schematic diagram of an embodiment of a battery module;

4 is a schematic diagram of an embodiment of the battery pack;

Figure 5 is an exploded view of Figure 4;

Fig. 6 is a schematic diagram of an embodiment of a device in which a lithium ion battery is used as a power source.

detailed description

The lithium ion battery according to the present application will be described in detail below.

The lithium ion of the present application includes a battery case, an electrolyte and an electrode assembly. The electrolyte includes a lithium salt and an organic solvent, and the electrode assembly is composed of a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode membrane which is arranged on at least one surface of the positive electrode current collector and includes a positive electrode active material. The negative electrode sheet includes a negative electrode current collector and a positive electrode film which is arranged on at least one surface of the negative electrode current collector and includes a negative electrode active material. Material negative diaphragm. The lithium salt includes one or more of the compounds represented by formula I, wherein n is an integer within 1 to 3, Rf ₁ and Rf ₂ are C _m F _2m+1 , where m is within 0 to 5. Rf ₁ and Rf _{2 are the} same or different, and the group margin of the lithium ion battery is 85%-95%.

The group margin of the lithium ion battery of the present application is 85%-95%. The group margin refers to the ratio of the actual internal cross-sectional area of the lithium-ion battery to the maximum internal cross-sectional area, that is, the filling rate, which can characterize the difficulty of the electrode assembly into the case and the pressure on the battery case after the electrode assembly is charged and expanded.

There are two ways to calculate the group margin, namely:

(1) Group margin = the overall cross-sectional area of the electrode assembly/the internal space area of the battery case;

(2) Group margin = thickness of electrode assembly/internal thickness of battery case.

The smaller the group margin of a lithium-ion battery, the easier it is for the electrode assembly to fit into the case, but the energy density of a lithium-ion battery with a smaller group margin is relatively low, which may not be able to meet actual usage requirements. The larger the group margin of the lithium-ion battery, the more difficult it is for the electrode assembly to enter the shell, which will not only increase the process difficulty but also cause damage to the electrode assembly; the lithium-ion battery with a large group margin has a relatively small proportion of electrolyte, so It will affect the cycle performance and rate performance of the lithium-ion battery; in addition, the electrode assembly in the lithium-ion battery with a large group margin will increase the pressure on the battery case after charging and expansion, so it will also deteriorate the safety performance of the lithium-ion battery . The group margin of the lithium ion battery of the present application is 85%-95%, which can enable the lithium ion battery to have a higher energy density without deteriorating the cycle performance, rate performance and safety performance of the lithium ion battery.

When the current common lithium ion batteries use conventional lithium hexafluorophosphate (LiPF ₆ ) as the lithium salt, because LiPF ₆ is easily decomposed at high temperatures and is extremely sensitive to moisture, it cannot be used in special environments with high energy density. At this time, lithium ion batteries usually perform Problems such as poor output rate performance, poor cycle performance, and poor safety performance are difficult to meet actual use requirements. The lithium ion battery electrolyte of the present application includes the imine-type lithium salt in Formula I, which can significantly improve the cycle performance, rate performance and safety performance of the lithium ion battery, and can improve the low temperature discharge performance of the lithium ion battery. This is because the thermal decomposition temperature of the imine-type lithium salt in formula I is usually greater than 200°C, which has the advantage of good thermal stability. At the same time, the imine-type lithium salt in formula I can also be lower than -20°C. Normal work; the imine-type lithium salt in formula I also has excellent electrical conductivity, the binding energy between Li ⁺ and imine anion is low, the dissociation degree of Li ⁺ is high, and the electrolyte can have a high Conductivity: The imine-type lithium salt in Formula I also helps to reduce the film-forming resistance on the surface of the positive and negative electrodes, and helps to form a stable and ion-conductive interface protective film on the surface of the positive and negative electrodes.

However, if the content of the imine-type lithium salt in formula I in the electrolyte is too low, the content of Li ⁺ in the electrolyte will be low, and the conductivity of the electrolyte will not be significantly improved, which will affect the cycle performance and rate performance of the lithium ion battery. The improvement is not obvious; if the content of the imine-type lithium salt in the formula I in the electrolyte is too high, the viscosity of the electrolyte will increase excessively, which is unfavorable for improving the cycle performance and low-temperature discharge performance of the lithium ion battery. In the lithium ion battery of the present application, the mass of the imine-type lithium salt in formula I is 5% to 25% of the total mass of the electrolyte, and within this range, the cycle performance, rate performance, and rate performance of the lithium ion battery can be improved simultaneously Low temperature discharge performance.

In a specific embodiment, the compound of Formula I may be selected from _{^{^{FSO 2 N - (Li +)}}} SO 2 F, FSO 2 N - (Li +) SO 2 CF 3, CF 3 SO 2 N - ( ^{_{_{li +) SO 2 CF 3,}}} FSO 2 N - (li +) SO 2 N - (li +) SO 2 F, FSO 2 N - (li +) SO 2 N - (li +) SO 2 N - (li ^{_{_{+) SO 2 F, FSO 2}}} N - (Li +) SO 2 N - (Li +) SO 2 CF 3, CF 3 SO 2 N - (Li +) SO 2 N - (Li +) SO 2 CF 3, _{^{^{FSO 2 N - (Li +)}}} SO 2 N - (Li +) SO 2 N - (Li +) SO 2 CF 3, CF 3 SO 2 N - (Li +) SO 2 N - (Li +) SO 2 N ^{-One or more of} (Li ⁺ )SO ₂ CF ₃ .

Among the lithium-ion batteries described in this application, although the lithium-ion battery itself may have good safety performance, it still has the general problem of nail penetration safety performance, especially for lithium-ion batteries with high energy density. Among them, the nail penetration safety performance of lithium-ion batteries is closely related to the performance of the positive electrode current collector. The smaller the thickness of the positive electrode current collector, the smaller the metal burrs formed on the positive electrode current collector after nail penetration, which is more conducive to improving the lithium ion battery However, if the thickness of the positive electrode current collector is too small, there may be a risk of strip breakage during the production process of the positive electrode sheet, which will cause the production to fail to proceed smoothly. Optionally, the thickness of the positive electrode current collector is 5 μm to 20 μm.

In the lithium ion battery described in this application, the elongation at break of the positive electrode current collector will also affect the nail penetration safety performance of the lithium ion battery. The greater the elongation at break of the positive electrode current collector, the larger the metal burrs formed on the positive electrode current collector after nail penetration. At the same time, the imine-type lithium salt in Formula I may also form larger burrs after corroding the positive electrode current collector. It is not conducive to improving the nail penetration safety performance of lithium-ion batteries; but if the elongation at break of the positive electrode current collector is too small, its ductility is difficult to meet the processing requirements, so it is not conducive to the processing and production of the positive electrode sheet. Optionally, the elongation at break of the positive electrode current collector is 0.8% to 4%.

In the lithium ion battery described in the present application, optionally, the positive electrode current collector is selected from aluminum foil. Since the imine-type lithium salt in Formula I will cause certain corrosion to the aluminum foil, an aluminum oxide layer can be provided on both surfaces of the aluminum foil to reduce the corrosion effect of the imine-type lithium salt in Formula I on the aluminum foil. Optionally, the thickness of the aluminum oxide layer is 5 nm-40 nm.

In the lithium ion battery described in this application, since the imine-type lithium salt in Formula I will cause corrosion to the positive electrode current collector, an appropriate amount of lithium hexafluorophosphate (LiPF ₆ ) can be added to the electrolyte to relieve the Corrosion effect of imine-type lithium salt on the positive electrode current collector However, the amount of LiPF ₆ should not be too large. This is because LiPF ₆ easily decomposes at high temperatures to generate HF and other gases. The generated gas will not only corrode the positive electrode active material, but also deteriorate the safety performance of the lithium ion battery. Optionally, the mass of LiFP ₆ is 0%-10% of the total mass of the electrolyte.

In the lithium ion battery described in the present application, the coating weight of the positive electrode sheet also has an impact on the energy density of the lithium ion battery. The greater the coating weight of the positive electrode sheet, the more obvious the energy density of the lithium ion battery is improved. However, if the coating weight of the positive sheet is too large, it is not conducive to the cycle performance and rate performance of the lithium-ion battery, and the coating weight of the positive sheet is too large to easily lead to lithium evolution inside the battery, thereby deteriorating the performance of the lithium-ion battery. Optionally, the single-sided coating weight of the positive electrode sheet is 0.015 g/cm ² to 0.023 g/cm ² .

In the lithium ion battery described in the present application, the positive electrode active material is selected from materials capable of extracting and inserting lithium ions. Specifically, the positive electrode active material can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and the above-mentioned compounds plus others One or more of compounds derived from transition metals or non-transition metals, but the application is not limited to these materials.

In the lithium ion battery described in this application, the positive electrode film may further include a conductive agent and a binder. The type and content of the conductive agent and the binder are not specifically limited, and can be selected according to actual needs. .

In the lithium-ion battery described in the present application, the negative electrode sheet may include a negative electrode current collector and a negative electrode membrane arranged on the negative electrode current collector and comprising a negative electrode active material, and the negative electrode membrane may be arranged in the negative electrode current collector. One surface can also be provided on both surfaces of the negative electrode current collector. The type of the negative electrode active material is not specifically limited, and can be selected from graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, elemental silicon, silicon-oxygen compounds, silicon-carbon composites, silicon One or more of alloys, elemental tin, tin oxide compounds, and lithium titanate. The negative electrode film may also include a conductive agent and a binder, wherein the type and content of the conductive agent and the binder are not specifically limited, and can be selected according to actual requirements. The type of the negative electrode current collector is not specifically limited, and can be selected according to actual needs.

In the lithium ion battery described in this application, the negative electrode sheet may also be metallic lithium or a lithium alloy.

In the lithium ion battery described in the present application, the separator is arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation. Wherein, the type of the isolation film is not specifically limited, and it can be any isolation film material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride and their multilayer composite film, but not limited to These ones.

In the lithium ion battery described in this application, the organic solvent may also include one or more of other types of chain carbonate, cyclic carbonate, and carboxylic acid ester. Among them, the types of chain carbonate, cyclic carbonate, and carboxylic acid ester are not specifically limited, and can be selected according to actual needs. Optionally, the organic solvent may also include diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, One or more of γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate, and tetrahydrofuran.

In the lithium ion battery described in the present application, optionally, the mass of the cyclic carbonate is less than or equal to 10% of the total mass of the electrolyte. Alternatively, the cyclic carbonate may include ethylene carbonate (EC). Ethylene carbonate is easy to oxidize and generates a large amount of gas, which poses a certain threat to the safety of lithium ion batteries. However, ethylene carbonate has a relatively high dielectric constant. If the content of conventional LiPF ₆ system is reduced, the conductivity will be great. influences. However, based on the imine-type lithium salt in formula I, because the anion and cation of this kind of lithium salt have a small effect, the electrolyte can still have good conductivity at a low EC content.

There is no particular limitation on the shape of the lithium ion battery in this application, and it can be cylindrical, square or any other shape. Fig. 1 shows a lithium-ion battery 5 with a square structure as an example.

In some embodiments, the battery case of the lithium ion battery may be a soft case, such as a pouch type soft case. The material of the soft bag can be plastic, for example, it can include one or more of polypropylene PP, polybutylene terephthalate PBT, polybutylene succinate PBS, and the like. The battery housing of the lithium ion battery may also be a hard shell, such as a hard plastic shell or a metal hard shell. Among them, the hard shell of metal material may be an aluminum shell, a steel shell, and the like. Optionally, the lithium ion battery housing is a hard shell made of metal.

In some embodiments, referring to FIG. 2, the battery case may include a case 51 and a cover plate 53. Wherein, the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the containing cavity, and a cover plate 53 can cover the opening to close the containing cavity.

The positive electrode sheet, the negative electrode sheet, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52.

The number of electrode assemblies 52 contained in the lithium ion battery 5 can be one or several, which can be adjusted according to requirements.

In some embodiments, lithium ion batteries can be assembled into battery modules, and the number of lithium ion batteries contained in the battery modules can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of lithium ion batteries 5 may be arranged in order along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of lithium ion batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having an accommodation space, and a plurality of lithium ion batteries 5 are accommodated in the accommodation space.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

4 and 5 are the battery pack 1 as an example. 4 and 5, the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. Multiple battery modules 4 can be arranged in the battery box in any manner.

Among the lithium-ion batteries described in this application, among the lithium-ion batteries with the same casing size, the greater the energy density of the lithium-ion battery, the more easily its cycle performance, rate performance, and safety performance are affected. The use of the imine-type lithium salt including I can achieve the purpose of improving the cycle performance, rate performance and safety performance on the basis of maintaining the high energy density of the lithium ion battery, thereby meeting actual use requirements. The lithium ion battery of the present application can maintain good cycle performance, rate performance and safety performance on the basis of maintaining a capacity not less than 150 Ah.

The third aspect of the present application also provides a device, which includes the aforementioned lithium ion battery of the present application. The lithium ion battery can be used as a power source of the device, and can also be used as an energy storage unit of the device. The device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

The device can select a lithium ion battery, battery module or battery pack according to its usage requirements.

Figure 6 is a device as an example. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the requirements of the device for high power and high energy density of the battery, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires light and thin, and can use lithium-ion batteries as a power source.

Hereinafter, the application will be further explained in conjunction with the examples. It should be understood that these embodiments are only used to illustrate the application and not to limit the scope of the application.

The lithium ion batteries of Examples 1-28 and Comparative Examples 1-9 were prepared according to the following methods

(1) Preparation of positive electrode sheet

The positive electrode active material LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are dissolved in the solvent N-methylpyrrolidone (NMP) in a weight ratio of 94:3:3 , After fully stirring and mixing uniformly, the positive electrode slurry is obtained; then the positive electrode slurry is uniformly coated on the positive electrode current collector, and then the positive electrode sheet is obtained after drying, cold pressing, and slitting. Among them, the parameters of the positive electrode current collector and the positive electrode sheet The coating weight is shown in Table 1.

(2) Preparation of negative electrode sheet

The active material artificial graphite, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) are dissolved in solvent deionized water in a weight ratio of 95:2:2:1 The negative electrode slurry is prepared by uniformly mixing with solvent deionized water; then, the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and the negative electrode film is obtained after drying, and then the negative electrode sheet is obtained by cold pressing and slitting.

(3) Preparation of electrolyte

In an argon atmosphere glove box (H ₂ O<0.1ppm, O ₂ <0.1ppm), the organic solvents shown in Table 2 are mixed in proportions, and then the fully dried lithium salt shown in Table 2 is dissolved in the organic In the solvent, an electrolyte is obtained.

(4) Preparation of isolation membrane

A conventional polypropylene film is used as the isolation film.

(5) Preparation of lithium ion battery

Lay the positive electrode sheet, the separator film, and the negative electrode sheet in order, so that the separator film is located between the positive and negative electrode sheets for isolation, and then wind to obtain the electrode assembly; place the electrode assembly in the battery case, and then inject it after drying Electrolyte, and then through the process of formation, standing still and other processes to make lithium-ion batteries. Among them, the group margin of lithium-ion batteries is shown in Table 3. The test method for the margin of the lithium ion battery group is as follows: the inner thickness of the test prismatic lithium ion battery shell is recorded as L1, the thickness of the test electrode assembly is recorded as L2, and the lithium ion battery group margin = L2/L1.

Table 1 Positive electrode parameter settings of Examples 1-28 and Comparative Examples 1-9

Table 2 Parameter settings of the electrolytes of Examples 1-28 and Comparative Examples 1-9

Next, the test procedure of the lithium ion battery is explained.

(1) Rate performance test of lithium ion battery

At 25°C, charge the lithium-ion battery with a constant current of 0.5C to 4.3V, then charge with a constant voltage of 4.3V until the current is less than 0.05C, and then discharge the lithium-ion battery at a constant current of 0.5C to 2.8V to obtain 0.5C Under the discharge capacity.

At 25℃, charge the lithium-ion battery at a constant current of 0.5C to 4.3V, then charge at a constant voltage of 4.3V until the current is less than 0.05C, and then discharge the lithium-ion battery at a constant current of 2C to 2.8V to obtain a 2C Discharge capacity.

Lithium ion battery 2C/0.5C rate performance (%)=(discharge capacity at 2C/discharge capacity at 0.5C)×100%.

(2) Cycle performance test of lithium ion battery

At 25℃, charge the lithium-ion battery with a constant current of 1C to 4.3V, then charge with a constant voltage of 4.3V until the current is less than 0.05C, and then discharge the lithium-ion battery with a constant current of 1C to 2.8V, which is a charge and discharge process. The charging and discharging are repeated in this way, and the capacity retention rate of the lithium ion battery after 1000 cycles is calculated.

The capacity retention rate (%) of the lithium ion battery after 1000 cycles at 25°C = (discharge capacity at the 1000th cycle/discharge capacity at the first cycle)×100%.

(3) Hot box safety performance test of lithium ion battery

At 25°C, charge the lithium-ion battery with a constant current of 1C to 4.3V, then charge with a constant voltage of 4.3V until the current is less than 0.05C, and the charging stops; put the lithium-ion battery in a hot box at a temperature of 5°C/min The heating rate is increased from 25°C to 150°C, and after reaching 150°C, the temperature remains unchanged, and then the timing is started until the surface of the lithium ion battery starts to smoke.

(4) Low temperature discharge performance test of lithium ion battery

At 25°C, charge the lithium-ion battery with a constant current of 1C to 4.3V, then charge with a constant voltage of 4.3V until the current is less than 0.05C, then discharge the lithium-ion battery with a constant current of 1C to 2.8V, and measure the lithium-ion battery’s The discharge capacity is recorded as the initial discharge capacity.

At 25°C, charge the lithium-ion battery to 4.3V at a constant current of 1C, then charge it at a constant voltage of 4.3V until the current is less than 0.05C, and then put the lithium-ion battery in a low temperature box at -20°C for 120 minutes Take it out and discharge it to 2.8V at a constant current of 1C, and record the discharge capacity of the lithium-ion battery after low-temperature storage.

Li-ion battery capacity ratio after low-temperature discharge (%) = (discharge capacity after low-temperature storage of lithium-ion/initial discharge capacity of lithium-ion battery at 25°C)×100%

(5) Nail penetration safety performance test of lithium ion battery

At 25°C, the lithium-ion battery is charged to 4.3V with a constant current of 1C, and then charged with a constant voltage of 4.3V until the current is less than 0.05C. At this time, the lithium-ion battery is in a fully charged state. A nail with a diameter of 3mm is used to test the lithium-ion battery at a speed of 150mm/s to observe whether the lithium-ion battery emits smoke, fires or explodes. If there are none, the lithium ion battery is considered to have passed the nail penetration test.

Table 3 Performance test results of Examples 1-28 and Comparative Examples 1-9

From the analysis of the test results in Table 2, it can be seen that the electrolyte of the lithium ion battery of Examples 1-28 includes imine lithium salt, and the content of the imine lithium salt in the electrolyte of the lithium ion battery of Examples 1-28 is moderate At this time, lithium-ion batteries have the advantages of good cycle performance, good rate performance, high safety performance, and good low-temperature discharge performance. At the same time, by adjusting the group margin of lithium-ion batteries in an appropriate range, lithium-ion batteries also take into account energy density High advantages.

Comparative Examples 1-3 only use conventional LiPF ₆ as the lithium salt, and the cycle performance, rate performance, safety performance, and low-temperature discharge performance of the lithium ion battery are all poor.

The elongation at break of the positive electrode current collector of the lithium ion battery of Comparative Example 4 is too low, which will cause the positive electrode sheet to be broken during the production process, and the production cannot be carried out properly.

The breaking elongation of the cathode current collector of the lithium ion battery of Comparative Example 5 is too high. Although the cycle performance, rate performance, and low-temperature discharge performance of the lithium ion battery can be improved to a certain extent, the excessively high breaking elongation of the cathode current collector The growth rate will reduce the nail penetration rate of the lithium-ion battery, making the lithium-ion battery a greater safety hazard.

The thickness of the positive electrode current collector of the lithium ion battery of Comparative Example 6 is too small, which will also cause the positive electrode sheet to be broken during the production process, and thus the production cannot be carried out properly.

The thickness of the positive electrode current collector of the lithium ion battery of Comparative Example 7 is too large. Similarly, although the cycle performance, rate performance, and low-temperature discharge performance of the lithium ion battery can be improved to a certain extent, the excessive thickness of the positive electrode current collector will also cause The nail penetration rate of lithium-ion batteries is reduced, making lithium-ion batteries a greater safety hazard.

The group margin of the lithium-ion battery of Comparative Example 8 is designed to be too small, and the 0.5C discharge capacity of the lithium-ion battery is relatively low, which makes it difficult to meet the actual use requirements of the lithium-ion battery.

The group margin of the lithium-ion battery of Comparative Example 9 is designed to be too large. Although the 0.5C discharge capacity of the lithium-ion battery can be improved, the rate performance, low-temperature discharge performance and cycle performance of the lithium-ion battery are all poor.

Based on the disclosure and teaching of the foregoing specification, those skilled in the art can also make changes and modifications to the foregoing embodiments. Therefore, this application is not limited to the specific implementations disclosed and described above, and some modifications and changes to this application should also fall within the protection scope of the claims of this application. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the application.

Claims

A lithium ion battery, including:

Battery case

Electrolyte, including lithium salt and organic solvent; and

The electrode assembly consists of a positive electrode sheet, a negative electrode sheet and a separator;

The positive electrode sheet includes a positive electrode current collector and a positive electrode membrane that is arranged on at least one surface of the positive electrode current collector and includes a positive electrode active material; the negative electrode sheet includes a negative electrode current collector and is arranged on at least one surface of the negative electrode current collector and includes a negative electrode active material. Material of the negative membrane;

among them,

The lithium salt includes one or more of the compounds represented by formula I;

Wherein, n is an integer within 1 to 3;

Rf 1 and Rf 2 are C m F 2m+1 , where m is an integer from 0 to 5, and Rf 1 and Rf 2 are the same or different;

The mass of the compound represented by formula I is 5% to 25% of the total mass of the electrolyte;

The group margin of the lithium ion battery is 85%-95%.
The lithium ion battery according to claim 1, wherein the compound of Formula I selected from FSO 2 N - (Li +) SO 2 F, FSO 2 N - (Li +) SO 2 CF 3, CF 3 SO 2 N - (Li +) SO 2 CF 3, FSO 2 N - (Li +) SO 2 N - (Li +) SO 2 F, FSO 2 N - (Li +) SO 2 N - (Li +) SO 2 N - (Li +) SO 2 F, FSO 2 N - (Li +) SO 2 N - (Li +) SO 2 CF 3, CF 3 SO 2 N - (Li +) SO 2 N - (Li +) SO 2 CF 3, FSO 2 N - (Li +) SO 2 N - (Li +) SO 2 N - (Li +) SO 2 CF 3, CF 3 SO 2 N - (Li +) SO 2 N - (Li + ) SO 2 N - (Li + ) in one or more of SO 2 CF 3.
The lithium ion battery according to claim 1 or 2, wherein the thickness of the positive electrode current collector is 5 μm to 20 μm.
The lithium ion battery according to any one of claims 1 to 3, wherein the elongation at break of the positive electrode current collector is 0.8% to 4%.
The lithium ion battery according to any one of claims 1 to 4, wherein the positive electrode current collector is selected from aluminum foil.
The lithium ion battery according to claim 5, wherein an aluminum oxide layer is provided on both surfaces of the aluminum foil.
The lithium ion battery according to claim 6, wherein the thickness of the aluminum oxide layer is 5 nm to 40 nm.
The lithium ion battery according to any one of claims 1-7, wherein the coating weight on one side of the positive electrode sheet is 0.015 g/cm 2 to 0.023 g/cm 2 .
The lithium ion battery according to any one of claims 1-8, wherein the compacted density of the positive electrode sheet is 2.0 g/cm 3 to 3.5 g/cm 3 .
The lithium ion battery according to any one of claims 1-9, wherein the mass of lithium hexafluorophosphate in the electrolyte is 0%-10% of the total mass of the electrolyte.
8. The lithium ion battery according to any one of claims 1-10, wherein the organic solvent comprises a cyclic carbonate, and the mass of the cyclic carbonate is less than or equal to 10% of the total mass of the electrolyte.
A device, wherein the drive source or storage source of the device is the lithium ion battery according to any one of claims 1-11.